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ZXSC300
SINGLE OR MULTI CELL LED DRIVER SOLUTION
DESCRIPTION The ZXSC300 is a single or multi cell LED driver designed for applications where step-up voltage conversion from very low input voltages is required. These applications mainly operate from single 1.5V or 1.2V battery cells. The circuit generates constant current pulses that are ideal for driving single or multiple LED's over a wide range of operating voltages. The ZXSC300 is a PFM controller IC that drives an external Zetex switching transistor with a very low saturation resistance. These transistors are the best switching devices available for this type of switching conversion enabling high efficiency conversion with input voltages below 1 volt. The drive output of the ZXSC controller generates a dynamic drive signal for the switching transistor. The circuit can start up under full load and operates down to an input voltage of 0.8 volts. The solution configuration ensures optimum efficiency over a wide range of load currents, several circuit configurations are possible depending on battery life versus brightness considerations. The ZXSC300 is offered in the SOT23-5 package which, when combined with a SOT23 switching transistor, generates a high efficiency small size circuit solution. The IC and discrete combination offers the ultimate cost vs performance solution for single cell LED driving applications.
FEATURES * * * * * 94% efficiency Minimum operating input voltage 0.8V Fixed output current Low saturation voltage switching transistor SOT23-5 package ORDERING INFORMATION DEVICE ZXSC300E5 Package SOT23-5 Partmarking C300
TYPICAL APPLICATION CIRCUIT
VBATT
L1
100H
U1
Vcc Vdrive Isense Gnd ZXSC300
Q1
FMMT617
LED1
WHITE LED
R1
0.33R
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ZXSC300
ABSOLUTE MAXIMUM RATING
Supply Voltage Maximum Voltage Other Pins Power Dissipation -0.3 to 10V -0.3 to VCC+0.3V 450mW Operating Temperature Storage Temperature -40 to 85C -55 to 125C
ELECTRICAL CHARACTERISTICS: Test conditions unless otherwise stated: VCC=1.5V, TAMB=25C
Symbol V CC Parameter Efficiency 1 Recommended supply voltage range Minimum startup and operating voltage Quiescent current 2 Base drive current Supply current High level drive voltage Low level drive voltage Output current reference voltage I SENSE voltage temp co. 2 I SENSE input current V ISENSE = 0V 0
3
Conditions
Min 0.8
Typ
Max 94 8
Units % V
V CC(min)
I DRIVE =-600A, V DRIVE =0.7V I DRIVE =-600A, V DRIVE =0.7V, T AMB =-10C 3 V DRIVE = 0.7V, V ISENSE = 0V V DRIVE = 0.7V, V ISENSE = 0V V ISENSE = 0V, I VDRIVE =-0.5mA V ISENSE = 50mV, I VDRIVE = 5mA 1.5 2 V CC -0.3 0 14
0.8 0.9 0.2
0.92
V
IQ I VDRIVE I CC V VDRIVE(high) V VDRIVE(low) V ISENSE (threshold) T CVISENSE I ISENSE
mA 3.6 4 V CC 0.2 mA mA V V mV %/C -65 A
19 0.4 -30
24
ELECTRICAL CHARACTERISTICS: AC PARAMETERS2 TEST CONDITIONS (Unless otherwise stated) ) VCC=1.5V, TAMB = 0 to 70C
Symbol T DRV F OSC
1 2
Parameter Discharge Pulse Width Recommended operating frequency 4
Conditions
Min 1.2
Typ 1.7
Max 3.2 200
Units s kHz
Application dependent, see reference designs. These parameters guaranteed by Design 3 Total supply current =IQ + IVDRIVE, see typical characteristics 4 Operating frequency is application circuit dependent. See applications section.
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ZXSC300
FMMT617
For the circuits described in the applications section, Zetex FMMT617 is the recommended pass transistor. The following indicates outline data for the transistor, more detailed information can be found in the Zetex surface mount data book or at www.zetex.com
ELECTRICAL CHARACTERISTICS (at TA = 25C unless otherwise stated).
PARAMETER Collector-Emitter Saturation Voltage Collector-Emitter Breakdown Voltage SYMBOL MIN. V CE(sat) TYP. 8 70 150 18 MAX. 14 100 200 UNIT mV mV mV V CONDITIONS. I C =0.1A, I B =10mA* I C =1A, I B =10mA* I C =3A, I B =40mA* I C =10mA*
V (BR)CEO 15
*Measured under pulsed conditions. Pulse width=300s. Duty cycle 2%
ZHCS1000
For the circuits described in the applications section Zetex ZHCS1000 is the recommended Schottky diode. The following indicates outline data for the diode, more detailed information is available at www.zetex.com
ELECTRICAL CHARACTERISTICS (at Tamb = 25C unless otherwise stated).
PARAMETER Forward Voltage Reverse Current Reverse Recovery Time SYMBOL VF IR t rr 50 12 MIN. TYP. MAX. 400 500 100 UNIT mV mV A ns CONDITIONS. I F =500mA I F =1A V R =30V Switched from IF = 500mA to IR = 500mA. Measured at IR=50mA
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ZXSC300
TYPICAL CHARACTERISTICS
300
4m
Quiescent Current (A)
200
Drive Current (A)
3m 2m 1m 0 1
100
0 1
2
3
Quiescent Current v Input Voltage
30m 100 25m
Input Voltage (V)
4
5
6
7
8
2
3
Drive Current v Input Voltage
Input Voltage (V)
4
5
6
7
8
Sense Voltage (V)
15m 10m 5m 0 1 2 3
Efficiency (%)
4 5 6 7 8
20m
95
90
Sense Voltage v Input Voltage
Input Voltage (V)
85 1.0
1.5
Input Voltage v Efficiency
Input Voltage (V)
2.0
2.5
3.0
3.5
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ZXSC300
DEVICE DESCRIPTION
The ZXSC300 is PFM, controller IC which, when combined with a high performance external transistor, enables the production of a high efficiency boost converter for use in single cell LED driving applications. A block diagram is shown for the ZXSC300 in Figure 1. With every on pulse the switching transistor is kept on until the voltage across the current-sense resistor exceeds the threshold of the ISENSE input. The on-pulse length, and therefore the switching frequency, is determined by the programmed peak current, the input voltage and the input to output voltage differential. See applications section for details. The Driver circuit supplies the external switching transistor with a fixed drive current. To maximise efficiency the external transistor switched quickly, typically being forced off within 30ns.
Pin out Diagram
Figure 1 ZXSC300 Block Diagram The on chip comparator forces the driver circuit and therefore the external switching transistor off if the voltage at ISENSE exceeds 19mV. This threshold is set by an internal reference circuit and divider. The Voltage at ISENSE is taken from a current sense resistor connected in series with the emitter of the switching transistor. A monostable following the output of the comparator forces the turn-off time of the output stage to be typically 1.7s. This ensures that there is sufficient time to discharge the inductor coil before the next on period.
VCC GND
1 2 3 Top View
5 4
VDRIVE ISENSE
Pin Descriptions
Pin No. 1 2 3 4 5 Name V CC Gnd N/C I SENSE V DRIVE Description Supply voltage, generally Alkaline, NiMH or NiCd single cell Ground Not connected Inductor current sense input. Internal threshold voltage set to 19mV. Connect external sense resistor Drive output for external switching transistor. Connect to base of external switching transistor.
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ZXSC300
REFERENCE DESIGNS
Two typical LED driving applications are shown. Firstly a maximum brightness solution and secondly an optimised battery life solution.
Maximum brightness solution
This circuit provides a constant current output to the LED by rectifying the switching pulses. This ensures maximum LED brightness.
VBATT
L1
100H
D1
ZHCS1000
U1
Vcc Vdrive Isense Gnd ZXSC300
Q1
FMMT617
C1
2.2F
LED1
WHITE LED
R1
0.1R
Material List
Ref U1 Q1 D1 R1 C1 L1 LED1 Value N/A N/A 1A 100m 2.2F 100H 5600mcd Part Number ZXSC300E5 FMMT617 ZHCS1000 Generic Generic DO1608P-104 NSPW500BS Manufacture Zetex Plc Zetex Plc Zetex Plc Various Various Coilcraft Nichia Comments Single cell converter, SOT23-5 Low V CE(sat) NPN, SOT23 1A Shottky diode, SOT23 0805 Size Low ESR ceramic capacitor Surface mount inductor White LED
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ZXSC300
Maximum battery life solution
To ensure optimum efficiency, and therefore maximum battery life, the LED is supplied with a pulsed current. Maximum efficiency is ensured with the removal of rectifier losses experienced in the maximum brightness solution.
100
VBATT
L1
100H
Single LED Load
Efficiency (%)
U1
Vcc Vdrive Isense Gnd ZXSC300
Q1
FMMT617
95
LED1
WHITE LED
90
R1
0.33R
85
1.0
1.5
2.0
2.5
3.0
3.5
Input Voltage (V)
Input Voltage v Efficiency
Materials list
Ref U1 Q1 R1 L1 LED1 Value N/A N/A 330m 100H 5600mcd Part Number ZXSC300E5 FMMT617 Generic DO1608P-104 NSPW500BS Manufacture Zetex Plc Zetex Plc Various Coilcraft Nichia Comments Single cell converter, SOT23-5 Low V CE(SAT) NPN, SOT23 0805 Size Surface mount inductor White LED
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ZXSC300
APPLICATIONS INFORMATION
The following section is a design guide for optimum converter performance. Switching transistor selection The choice of switching transistor has a major impact o n th e c onver t er e f f i c i enc y. For o p t i m u m performance, a bipolar transistor with low VCE(SAT) and high gain is required. The Zetex FMMT617 is an ideal choice of transistor, having a low saturation voltage. A data sheet for the FMMT617 is available on Zetex web site or through your local Zetex sales office. Outline information is included in the characteristics section of this data sheet.
Schottky diode selection
For the maximum battery life solution a Schottky rectifier diode is required. As with the switching transistor the Schottky rectifier diode has a major impact on the converter efficiency. A Schottky diode with a low forward voltage and fast recovery time should be used for this application. The diode should be selected so that the maximum forward current is greater or equal to the maximum peak current in the inductor, and the maximum reverse voltage is greater or equal to the output voltage. The Zetex ZHCS1000 meets these needs. Datasheets for the ZHCS Series are available on Zetex web site or through your local Zetex sales office. Outline information is included in the characteristics section of this data sheet. For the maximum brightness solution a pulsed current is supplied to the LED therefore a Schottky rectifier diode is not required. Inductor selection The inductor value must be chosen to satisfy performance, cost and size requirements of the overall solution. For the reference designs we recommend an inductor value of 100uH with a core saturation current rating greater than the converter peak current value and low series resistance.
Inductor selection has a significant impact on the converter performance. For applications where efficiency is critical, an inductor with a series resistance of 500m or less should be used. Peak current definition The peak current rating is a design parameter whose value is dependent upon the overall application. For the high brightness reference designs, a peak current of was chosen to ensure that the converter could provide the required output power to the LED. In general, the IPK value must be chosen to ensure that the switching transistor, Q1, is in full saturation with maximum output power conditions, assuming worse-case input voltage and transistor gain under all operating temperature extremes. Once IPK is decided the value of RSENSE can be determined by: RSENSE = VISENSE IPK
where VISENSE=19mV
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ZXSC300
Output Power Calculation
By making the above assumptions for inductance and peak current the output power can be determined by: POUT = (VOUT- VIN) x (IPK + IMIN) TOFF x (TON + TOFF ) 2 Capacitor selection For pulsed operation, as in the maximum battery life solution, no capacitors are required at the output to the LED. For rectified operation, as in the maximum brightness solution, a small value ceramic capacitor is required, typically 2.2uF. Generally an input capacitor is not required, but a small ceramic capacitor may be added to aid EMC, typically 470nF to 1uF. Demonstration board A demonstration board for the Maximum battery life solution, is available upon request. These can be obtained through your local Zetex office or through Zetex web pages. For all reference designs Gerber files and bill of materials can be supplied.
Note: VOUT = output voltage + Schottky rectifier voltage drop
where TOFF 1.7s (internally set by ZXSC300) and TON = and IMIN = IPK - ( VOUT - VIN ) x TOFF L TOFF (VOUT - VIN) VIN
Operating frequency can be derived by: 1 F= (TON + TOFF )
Layout of Maximum battery life solution Top Copper Drill Holes
Bottom Copper
Silk Screen
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ZXSC300
(Notes)
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ZXSC300
Supplier Listing
GERMANY Zetex GmbH Munich (49) 894549490 ASIA Zetex Asia Hong Kong (852) 2610 0611 AVX Asia Singapore (65) 258 2833 http://www.avxcorp.com Coilcraft http://www.coilcraft.com Nichia Corporation Nichia Europe B.V. Amsterdam The Netherlands (31) 20 5060900 Nichia Corporation Tokyo Sales Office Tokyo, Japan (81) 3 3456 3784 Nichia America Corporation Head Office (1) 717 285 2323 San Jose (1) 408 573 0933 Coilcraft Inc (1) 847 639 6400 Coilcraft Europe (44) 1236 730595 USA Zetex Inc Long Island NY (1) 631 543 7100 AVX USA (1) 843 448 9411 UK Zetex PLC Chadderton, Oldham (44) 161 622 4444 AVX UK (44) 1252 770000
Zetex
http://www.zetex.com AVX
http://www.nichia.co.jp
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ZXSC300
PACKAGE DIMENSIONS SOT23-5
DIM Millimetres MIN A A1 A2 b C D E E1 e e1 L a 0.90 0.00 0.90 0.35 0.09 2.80 2.60 1.50 0.95 REF 1.90 REF 0.10 0 0.60 10 MAX 1.45 0.15 1.3 0.50 0.20 3.00 3.00 1.75 Inches MIN 0.035 0.00 0.035 0.014 0.0035 0.110 0.102 0.059 0.037 REF 0.075 REF 0.004 0 0.024 10 MAX 0.057 0.006 0.051 0.020 0.008 0.118 0.118 0.069
Zetex plc. Fields New Road, Chadderton, Oldham, OL9-8NP, United Kingdom. Telephone: (44)161 622 4422 (Sales), (44)161 622 4444 (General Enquiries) Fax: (44)161 622 4420 Zetex GmbH Streitfeldstrae 19 D-81673 Munchen Germany Telefon: (49) 89 45 49 49 0 Fax: (49) 89 45 49 49 49 Zetex Inc. 47 Mall Drive, Unit 4 Commack NY 11725 USA Telephone: (631) 543-7100 Fax: (631) 864-7630 Zetex (Asia) Ltd. 3701-04 Metroplaza, Tower 1 Hing Fong Road, Kwai Fong, Hong Kong Telephone:(852) 26100 611 Fax: (852) 24250 494 These are supported by agents and distributors in major countries world-wide (c) Zetex plc 2001 www.zetex.com
This publication is issued to provide outline information only which (unless agreed by the Company in writing) may not be used, applied or reproduced for any purpose or form part of any order or contract or be regarded as a representation relating to the products or services concerned. The Company reserves the right to alter without notice the specification, design, price or conditions of supply of any product or service. Publication Ref. SCZXSC300DS
ISSUE 1 - JUNE 2001 12

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